MONOSACCHARIDES

From Big Medical Encyclopedia

MONOSACCHARIDES (synonym: monoses, simple carbohydrates) — the carbohydrates not capable to hydrolytic decomposition; whether you will present nek-ry of monosaccharides (glucose, fructose, etc.) play in an animal organism an important role biol, fuels also are base units of highly specialized, and also structural and reserve biopolymers (nucleinic to - t, a glycogen, starch, etc.). At disturbance of exchange of any M. in a human body its concentration increases in biol, liquids that is important diagnostic test (see. Galactosemia , diabetes mellitus , Melituria , Fruktozemiya ).

General formula of most of M. of C n H 2n O n . On number of carbon atoms all M. are divided into trioses (glitseraldegid, dihydroxy acetone), tetroses (erythrose, threose), pentoses (see), hexoses (see), heptoses (e.g., sedoheptulose), octoses, nonoza and thecoses.

M are the polyatomic alcohol containing aldehydic (— CHO) or ketonic (With = O) groups; therefore M. are divided into aldoses (or aldosugar, napr, glucose) and a ketosis (or ketosugar, napr, fructose). M can exist both in an acyclic form, and in the form of hemiacetal cycles — six-membered (pyranosides) and five-membered (furanozida). Conformation (see) pyranosides can be various; two forms of piranozny rings are stablest: form of the boat (B-form; English boat boat) and form of a chair (C-form; English chair chair). From them the form of a chair as it contains the smallest number of the hydrogen atoms «covering» each other is more resistant. Depending on a spatial relationship of hydroxylic group — OH and atom — H at the first carbon atom distinguish alpha and beta forms M.; between these forms M. in solution labile equilibrium is established (see. Isomerism ). According to an arrangement of atoms — H and OH-group at the last asymmetric carbon atom distinguish D-and L-ranks M. Each group M. with this or that number of carbon atoms contains a certain number of asymmetric carbon atoms (at their aldohexoses 4, at ketohexoses 3). The number of asymmetric carbon atoms and an arrangement around them of OH-group and atoms — H defines amount of possible stereoisomers M. (at aldohexoses of 16 stereoisomers: D-glucose, a D-galactose, D-mannose etc., at ketohexoses of 8 stereoisomers: D-fructose, D-sorbose, etc.). Such M. belong to M. also deoxysugar, i.e., at to-rykh one or two spirit hydroxylic groups are replaced with hydrogen (e.g., desoxyribose), and aminosugar, i.e. such M., at to-rykh hydroxylic group is replaced with an amino group (e.g., a glycosamine, neuraminic to - that, etc.).

M represent colourless crystal substances, usually sweet on taste, well water soluble, it is worse — in alcohol, insoluble in acetone and ether. They have optical activity, are reactive at the expense of the carbonyl group. At oxidation of aldose give aldonic, sugar and uranium to - you, a ketosis collapses. M can give hydrazones, osazones and triazoles; at recovery of carbonyl group of M. give polyatomic alcohol, at substitution of hydroxylic groups M. form glycosides (see), simple and esters. Receive M. hydrolysis poly-and oligosaccharides and is more rare chemical synthesis. Quantitatively and qualitatively M. determine by the reducing ability, optical activity, formation of furfurals in to - those, condensation with arylamines, enzymatic methods and so forth

M. are eurysynusic in the nature both in a free look, and in the form of derivatives (phosphate ethers, nukleoziddifosfata, glycosides, etc.).

See also Glucose , Mannose , Neuraminic acid , Fructose .


Bibliography: Kochetkov N. K., etc. Chemistry of carbohydrates, M., 1967; Stepanenko B. N. Chemistry and biochemistry of carbohydrates (monosaccharides), M;, 1977.


V. K. Gorodetsky.

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